If you are going to be in the area for less than 3 months (while on holiday or temporary business for example) you can ask a GP to accept you as a temporary resident. You remain on the list of your own GP but can be treated by the temporary GP should need arise. You will not be issued with a medical card and your medical records will not be transferred to your temporary doctor.
If you cannot find a GP willing to accept you contact your Health Authority/Board. They will probably give you a list of GPs to try and ask you to contact at least three yourself. If you still cannot get accepted the Health Authority/Board will allocate you to a GP. The GP is obliged to accept you - at least on a temporary basis.